Evaporative process using submerged combustion



Nov. 2, 1965 w. v. BAUER 3,215,189

EVAPORATIVE PROCESS USING SUBMERGED COMBUSTION Filed May l5, 1965 Unted States Patent O 3,215,189 EVAPORATIVE PRCESS USING SUBMERGED COMBUSTION William V. Bauer, Scarsdale, N.Y., assignor to The Lummus Company, New York, N.Y., a corporation of Delaware Filed May 13, 1963, Ser. No. 279,734 7 Claims. (Cl. 159-16) The present invention relates to an evaporation process and apparatus therefor, and more particularly, the present invention relates to a multiple-effect evaporation process and apparatus therefor wherein submerged combustion techniques are utilized to generate steam from waste brine for the rst effect of the multiple-effect evaporator.

While the subject invention will be described in connection with saline water conversion, it will be apparent that the invention may also be applied to the production of potable water from brackish water, and to the concentration of other brines.

As taught in copending application of Guerrieri et al. Serial No. 243,319 I'iled December 10, 1962, the use of submerged combustion techniques to generate the steam required in the first effect of a multiple-effect evaporation process offers several advantages. For example, a submerged combustion unit results in higher thermal efficiencies as compared to conventional boilers since the combustion products are in direct contact with the liquid thereby affording better heat transmission and enabling the temperature of the euent gas to closely approach the temperature of the boiling liquid. Furthermore, since the steam for the first effect is generated from otherwise waste brine, it is not necessary to use part of the product water stream, as is the case when a conventional boiler and steam turbine power cycle to supply the steam requirements of the rst effect. Additionally, the amount of the waste brine stream and the waste disposal costs are reduced which may be considerable economic factors at inland installations.

The gaseous effluent from a submerged combustion unit consists of steam and non-condensible gases. Consequently, to condense a major portion of the steam, a relatively high pressure must be maintained in the condenser, which requires that submerged combustion be conducted at a high pressure with an expenditure of a considerable amount of energy to compress the combustion air and fuel. The power requirements for compressing the air alone, in a plant producing l million gallons of water per day, are in the order of 16,000 H.P. With procedures heretofore available, such a power requirement is supplied by essentially conventional external power cycles, such as a boiler and a steam turbine for driving the compressors. Generally, the efficiency of such external power cycles is low, in the order of 25% The present invention proposes to utilize submerged combustion techniques in a multiple-effect evaporation system in such a manner as to achieve a power balance thereby obviating the necessity of an external power cycle. In accordance with my invention, a portion of the waste brine from the last effect of the multiple-effect evaporator (hereinafter referred to as the last eifect) is passed to a submerged combustion unit. The waste brine is preferably preheated prior toy introduction into the submerged combustion unit. Air and fuel are compressed and burned in the unit. The pressure Vto which the air and fuel are compressed depends upon the number of evaporative effects, and primarily the pressure to be maintained in the first effect of the multiple-effect evaporator. The steam and non-condensible combustion products are withdrawn from the submerged combustion unit and are passed through a super-heater, and thence to a high pressure turbine for partial power recovery. The pressure at which the submerged combustion unit is operated and the condensation pressure of the initial effect are maintained at levels such that the gaseous effluent from the submerged combustion unit, after being superheated and expanded in the high pressure turbine, will be at a temperature and pressure required in the initial effect to achieve the desired condensation of the water vapor contained in the effluent. The power developed in such turbine and the powe-r developed in Subsequent low pressure turbines within the system furnish the power requirements of the fuel and air compressors. Consequently, the power necessary to drive the compressors is provided by the expansion of various process streams, thus eliminating the need for external power cycles, except during startup.

The steam and combustion products mixture leaving the high pressure turbine is passed to the initial effect of the multiple-effect evaporator (hereinafter referred to as the initial effect). Steam condensate is separated from the remaining gases leaving the initial effect and the remaining gases are then passed with or without reheating through low pressure turbines for additional power recovery. The efficiency of the power cycle, in accordance with my invention, is substantially greater than the eiliciency of an external power cycle, and is in the order of from 50% to 60%, being the product of the thermal efficiencies of the superheater and high pressure turbine. Overall efficiency of a system using an external power cycle is usually no greater thanvabout 25%. The temperature of the gas and the condensate leaving the initial effect is selected so as to provide a AT across the evaporator heat exchange surface sufficiently high to compensate for the lower overall heat transfer coefficient of the gas produced in the submerged combustion unit as a result of the presence of non-condensible components in the gas. Further, the pressure of the gas leaving the initial effect is selected so as to achieve condensation of an amount of water approximately equal to the amount of water evaporated in the submerged combustion unit, thereby generating sufficient vapor for the second effect of the multiple-effect evaporator. The amount of Water that must be evaporated in the submerged combustion unit and condensed in the initial effect depends upon the number of effects, materials of construction and economic factors.

One of the objects of the present invention is to provide an improved multiple-effect evaporation system of increased efficiency.

Another object of the present invention is to utilize submerged combustion techniques to provide the heating medium for the initial effect of a multiple-effect evaporation system having no external power cycle requirements.

A further objectof the present invention is to provide a method for generating steam from waste brine in a submerged combustion burner, and for utilizing the resulting steam and combustion products mixture to supply heat to an evaporator and to provide the power required for the compressors supplying air and fuel gas to the burner.

These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawing.

The sole gure of the drawing is a schematic flow diagram of one embodiment of the present invention illustrating only the initial and last effects of a multiple-effect evaporation system, since multiple-effect evaporators are well known in the art.

Referring now to the drawing, an initial effect 10 and a last effect 12 are illustrated having heat exchange surfaces, generally designated as 11 and 13, respectively. Saline water, brackish Water or other brine feed is passed to the initial effect through feed line, generally designated asp14. The feed in line 14V is preheated in a known manner byV passage through a series of heat exchangers associated with each effect, such as the heat exchangers 16, 18, 20 and 22 of the last effect, and heat exchangers 24 and 26 of the initial effect. In the abovementioned heat exchangers, the feed is heated either by the conden- -sate in the main product line, generally designated 28, or by condensing steam from one or more of the evaporative effects.l

In the initial effect 10, a portion of the preheated feed from line 14 is vaporized at the heat exchange surface 11, by indire-ct heat exchange with a heating medium consisting of a high pressure mixture of steam and non-condensible combustion pnoducts supplied to the heat exchange surface 11 through line 30, as hereinafter described. The vapor generated in initial effect 10 is Withdrawn through line 32. A major portion of lthe vapor in line 32 is passed via line 34 to the heat transfer surface of the second effect (not shown) to supply the heating requirement of that effect, as is well known in theart. The remainder of the vapor in line 32 is condensed in heat exchanger 24 in the process of preheating the feed in line 14. Condensate from heat exchanger 24 is passed through line 36 to the main product recovery line 28. The heating medium in line 30 passing through heat exchange surface 11 is withdrawn from the initial effect 10 through line 38 for further processing as hereinafter described. The partly concentrated feed is withdrawn from initial effect 10 through line 40 and is passed to a subsequent evaporative effect (not shown) for additional concentration.

Eventually the concentrated feed is passed to the last effect 12 through line 42 from the preceding evaporative effect. A major portion of the steam generated in the preceding effect is passed into the heat exchange surface 13 of the last effect 12 through line 44. A minor portion of the steam in line 44 is withdrawn through line 46 and is pass-ed to condenser 20 for preheating the feed in line 14. Condensate from condenser 20 is passed through line 48 to the main product recovery line 28. The vapor generated in the last effect 12 is Withdrawn through line 50 and is passed to a condenser 52. Condensate from condenser 52 is withdrawn and passed through line 54 into the porti-on of product recovery line 28 between heat exchangers 16 and 18. A steam ejector 56 or other suitable vacuum producing means maintains a vacuum on a deaerator 58 through line 60 whereby the feed in line 14 is deaerated during passage through fthe deaerator 58. Condenser 52 is in communication with evacuator 56 through lines 62 and 60.

The concentrated brine is withdrawn from the last 'effect 12 through line 64 and a portion thereof is disposed through waste line 66. Another portion of the 'brine is passed through line 68 by pump 70and is passed 'in line 72 serially through heat exchangers 76, 78 and 80 for preheating prior to introduction in to submerged combustion unit 74. Air for sustaining combustion in submerged combustion unit 74 is compressedin stages in compressors 82, 84 and 86. The compressed air from the `first stage compressor 82 is passed through line 88 to heat exchanger 76, and then through line 90 and cooler 92 to the second stage compressor 84. Similarly, the compressed air from compressor 84 is passed through line 94 to heat exchanger 78, and then through line 96 land cooler 98 to compressor 86. The above arrangein successive stage-s and intercooled between stages prior pressors 84 and 86 may be of the centrifugal type for maximum economy.

ment enables the air for combustion to be compressed Y Combustion air from compressor 86 is introduced through line 100 into a burner housing 102 of the submerged combustion unit 74. A suitable fuel, such as natural gas, is passed through a compressor 104 and line 106 for admixture with the combustion air. Suitable control means (not shown) are provided to regulate air and fuel flow rates to insure complete combustion of the fuel. Combustion takes place in a burner section 108 of the submerged combustion unit 74 which extends down beneath the level of the brine within submerged combustion unit 74. As a result of the intimate Contact between the rising bubbles of the combustion products and the brine introduced into submerged combustion unit 74 through line 72, good thermal efficiency is achieved in the submerged combustion unit 74 and water is evaporated fnom the brine. Steam is also produced by the reaction of the oxygen in the air with the hydrogen constituent of the hydrocarbon fuel. Since a high pressure is maintained in the submerged combustion unit 74, steam of relatively high temperature and pressure is produced. As hereinbefore mentioned, the pressure maintained in the `submerged combustion unit 74 is selected as required by the number of evaporative effects in the system, as well as 'other factors.

The steam and non-condensible combustion products are removed from submerged combustion unit 74 through line 110 and are passed to a knockout drum 112 to minimize brine carry-over. The non-condensible combustion products consist primarily of nitrogen and carbon dioxide formed by the oxidation of the carbon constituents of the fuel gas. Steam and non-condensible combustion products from knockout drum 112 are passed through line 114 to a Superheater 118. Superheater 118 may be of conventional construction and is provided With burner means (not shown) for heating the mixture of steam and non-condensible combustion products. The superheated steam, together with the heated non-condensible cornbustion products, is withdrawn from Superheater 118 and is passed through line 120 tol a high pressure turbine 122 of known construction which is provided with power take-olf means. The power generated in turbine 122 provides a portion of the power requirements of the air compressors 82, 84 and 86, and fuel compressor 104. The expanded steam and non-condensible combustion products from turbine 122, still at a relatively high pressure, are introduced into the initial effect 10 through line 30.

An auxiliary boiler 124 may be provided to supply steam to the system at start-up through line 126.

As previously stated, the steam and non-condensible combustion products in line 30 constitute the heating medium for the initial effect 10, and are withdrawn from initial effect 10 through line 38 and introduced into tank 128 to separate condensate therefrom. Condensate is withdrawn from tank 128 through 130 and is passed int-o the main product recovery line 28. The pressure 'of the gas in line 38 is determined by the requirement of condensing an amount of steam in the initial effect 10 approximately equal to the amount of water evaporated in the submerged combustion unit 74, and is generally in the range of from about 150 to 200 p.s.i.a. The gas withdrawn from tank 128 through line 132 contains a substantial amount of water vapor and is passed through line 132 to a low pressure expander 134 for additional power recovery, and thence through line 136 to tank 138.

In tank 138, additional condensate is separated and passed through line 140 to be combined with the condensate in line 130. The remaining gas, including steam, is passed through line 142 to a second low pressure ex- ;pander 144 for additional power recovery, and is then passed to tank 146 through line 148 wherein additional -condensate is separated. The non-condensible combustion products are exhausted from tank 146 through vent line 150. Condensate is withdrawn from tank 146 through line 152. A portion of the condensate in line 152 is passed through line 154 by pump 156, and thence through line 158 to an economizer section of superheater 118, generally designated as 160, to extract additional heat from the hot exhaust gases in superheater 118. The resulting steam is withdrawn from the economizer sec- 'tion 160 and is passed through lines 162 and 126 to be combined with the steam and the non-condensible cornbustion products in line 114 being introduced into the superheater 118.

The highly concentrated brine in submerged combus tion unit 74 is Withdrawn through line 164 which is provided with suitable valve means 166 controlled, as shown, by a float valve in unit 74, for maintaining the brine level in unit 74 above the bottom end of burner section 108. The brine in line 164 is passed into a flash tank 168 maintained at substantially atmospheric pressure. The resulting steam is passed through line 170 and is condensed in heat exchanger 80. The condensate from heat exchanger 80 is passed through line 172 to tank 174. From tank 174, the condensate is Withdrawn through line 176 by pump 178 and is passed through line 180 to be combined with the condensate from tank 138 in line 140. Tank 174 is also connected to steam ejector 56 via line 182. The remaining brine in flash drum 168 is pumped to discharge through line 184 by pump 186.

While the manner of application of the invention may be varied widely, particularly with respect to specific operating temperatures and pressures, the example below will serve to illustrate the present invention with respect to an installation designed to produce million gallons of water per day. A multiplicity of submerged combustion burners is required to meet the process demands.

Example 1,114,800 pounds per hour of brine having a concentration of 13.8% by weight of salt and at a temperature of 119 F. are withdrawn from the last effect 12 of a twelve effect multiple-effect evaporator seystem. 358,000 pounds per hour of the brine are passed through heat exchangers 76, 78 and 80 wherein the brine is heated to a temperature of 200 F. and is introduced into the submerged combustion burner 74. 314,000 cubic feet per hour of natural gas (STP) having a net heating value of 912 B.t.u./s.c.f., and 3.17 106 cubic feet per hour of air (STP) are separately compressed to 400 p.s.i.a. and burned in the burner section 108 of the submerged combustion unit 74. 263,000 pounds per hour of water at a temperature of 425 F. are evaporated from the brine and, together with 251,440 pounds per hour of combustion products, are passed through knockout drum 112.

The steam and non-condensible combustion products are passed through superheater 118 wherein they are heated to a temperature of 547 F. and thence expanded through high pressure turbine 122 from which they are discharged at a temperature of 365 F. and at a pressure of 157 p.s.i.a., generating 10,400 H.P. by such expansion. The steam and non-condensible combustion products are then introduced into the Isteam chest of the initial effect 10. 263,000 pounds per hour of steam are generated and Withdrawn through line 32, with a major portion being passed through line 34 to the second effect. 3,558,500 pounds per hour of water (or 10X106 gallons per day) at 99.6 F. are withdrawn through product line 28.

265,900 pounds per hour of a gaseous effluent containing 17.2% steam at a pressure of 149.5 p.s.i.a. and a temperature of 265 F. are expanded through low pressure turbine 134 to a pressure of 47.5 p.s.i.a. thereby generating 4,400 H.P. The effluent from the low pressure turbine 134 is then passed to low pressure turbine 144 wherein the gas is further expanded to 14.9 p.s.i.a. generating 3,770 H.P. The power generated in the high pressure turbine 122, and the low pressure turbines 134 and 144 totals 18,570 H.P., and is slightly greater than 6 the power requirements of the compressors which total 18,510 H.P.

96,000 pounds per hour of concentrated brine containing 26.5% dissolved salt andV 32.4% solid salt in suspension are withdrawn through the submerged combustion unit 74 through line 164 and are introduced into flash drum 168 maintained at atmospheric pressure. 12,950 pounds per hour of steam are Withdrawn from drum 168 through line 170 and 83,050 pounds per hour of concentrated brine containing 26.5% dissolved solids and 44.6% undissolved solids are withdrawn and discharged through line 184.

The present invention is not limited to the purification of saline water, but may be applied to the concentration of other brines. Also, while the invention is shown as applied to a conventional multiple-effect evaporator system, it is apparent that the evaporator system may be of a combined type utilizing both multiple-effect evaporation and vapor compression evaporators.

While I have shown and described a preferred form of my invention, I am aware that variations may be made thereto and I, therefore, desire a broad interpretation of my invention within the scope of the disclosure herein and the following claims.

I claim:

1. An evaporation system `comprising a multiple-effect evaporator including an initial effect and a last effect, a submerged combustion unit, conduit means for passing brine from said last effect to said unit, means including compressor means for supplying combustion air and fuel to said unit for combustion therein, a superheater for heating the gases and vapors leaving said unit, a flash vaporizer receiving concentrated brine from said unit, means for separating flashed water vapor from said concentrated brine, a high pressure turbine driven by the expansion of the superheated gases, conduit means for supplying the expanded gases from said turbine to said initial effect for indirectly vaporizing water from the feed brine Within said initial effect, means for separating condensate from said gases and vapors leaving the initial effect, at least one low pressure expander, and conduit means for supplying the gases and remaining vapors to said low pressure expander for additional power recovery.

2. An evaporation system comprising a multiple-effect evaporator including an initial effect and a last effect, 'a submerged combustion unit, a conduit for passing brine from said last effect to said unit, means including compressor means for supplying combustion air and fuel to s-aid unit for combustion therein, a superheater for heating the gases and vapors leaving said unit, a high pressure turbine driven by the expansion of superheated gases to provide power for said -compressor means, conduit means for supplying the expanded gases and vapors to said initial effect for vaporizing water from the feed brine Within said initial effect, means for separating condensate from the remainder of said gases and vapors, low pressure expanders, conduit means for supplying the gases and vapors to said low pressure expanders for additional power recovery, means for separating and recovering additional condensate from the gases after each of said low pressure expanders, and means for supplying at least part of said additional condensate to said superheater to generate steam.

3. An evaporation system comprising a multiple-effect evaporator including an initial effect and a last effect, a submerged combustion unit, a conduit passing brine from said last effect to said unit, means including compressor means for supplying combustion air and fuel to said unit for combustion therein, a superheater for heating gases and vapors leaving said unit, a high pressure turbine driven by the expansion of superheated gases and vapors from said superheater to provide power for said compressor means, conduit means for supplying the expanded gases and vapors to said initial effect for vaporizing water from the feed brine within said initial effect, means for separating condensate from the remainder of said gases and vapors, low pressure expanders, conduit means for supplying the gases and remaining vapors to: said low pressure expanders for ad-ditional power recovery, means for separating and recovering additional condensate from the gases and remaining vapors after each of said low pressure expanders, and means for supplying at least part of said additional condensate to said superheater to generate steam, and means for combining the generated steam from said superheater with gases from said unit,

4. In a multiple-effect saline Water purication process, the steps of passing normally Waste brine from a last effect to a submerged combustion unit, generating steam from said brine by direct contact with hot products of combustion, superheating the steam and other gaseous products leaving said unit, passing said brine from said unit to 'a flash vaporizer, separating and recovering additional steam from said vaporizer, passing the superheated steam and other gaseous products to a high pressure turbine for expansion therein, using the power recovered by said turbine to drive compressors for compressing air supplied to said unit, producing water vapor in an initial eifect by indirect heat exchange with the expanded gases and vapors from said turbine, separating condensate from the gases and vapors, and passing the gases and remaining vapors through additional turbine means for power recovery.

5. In a multiple-effect evaporation process, the steps of passing normally waste brine from the last effect to a submerged combustion unit, generating steam from said brine by direct contact with hot products of combustion, superheating the steam and other gases and vapors leaving said unit, passing the superheated gases and vapors to a high pressure turbine for expansion therein, passing the expanded gases and vapors to an initial eifect, producing water vapor in a said initial effect by indirect heat exchange with said expanded gases and vapors, separating condensate from the gases and vapors, passing the gases and remaining vapors through additional turbine means for power recovery, separating additional condensate from the gases and remaining vapors, and passing at least part of said additional condensate to a preheating step prior to said superheating step to generate additional steam.

6. The process as claimed in claim 5, and additionally comprising combining the steam generated from said additional condensate in sai-d pre-heating step with the steam and other gases leaving said unit prior to said superheating.

7. In a multiple-etfect evaporation process, the steps of passing normally waste brine from the last effect to a submerged combustion unit, generating steam from said brine by direct contact with hot products of combustion at a pressure of about 365 p.s.i.a., passing the brine from said unit to a flash vaporizer, dashing off additional steam in said vaporizer, condensing said additional steam, superheating the steam and other gaseous products leaving the burner unit to about 547 F., passing the superheated steam land other gaseous products to a high pressure turbine for expansion therein to a pressure of about p.s.i.a, utilizing the power generated by said turbine to drive compressors for compressing fuel and combustion air supplied to said unit, passing the expanded 4gases and vapors to an initial eifect, producing Water vapor from the feed brine in a said initial effect by indirect heat exchange with said expanded gases and vapors, separating condensate from the cooled expanded gases and vapors, and passing the cooled expanded gases and remaining vapors through additional turbine means for power recovery.

References Cited by the Examiner UNITED STATES PATENTS 2,354,175 7/ 44 Wilcoxson. 2,524,753 10/50 Betts. 2,647,370 8/53 Miller.

2,759,882 8/56 Worthen et al. 159-24 2,764,234 9/ 56 Rauh. 2,770,295 11/56 Allen 159-47 X 2,839,122 6/ 58 Laguilharre. 2,889,683 6/59 Miller 60-39.57

OTHER REFERENCES Power Eng., pp. 92, 93, vol. 58, No. 6, June 1954.

NORMAN YUDKOFF, Primary Examiner. 

1. AN EVAPORATION SYSTEM COMPRISING A MULTIPLE-EFFECT EVAPORATOR INCLUDING AN INITIAL EFFECT AND A LAST EFFECT, A SUBMERGED COMBUSTION UNIT, CONDUIT MEANS FOR PASSING BRINE FROM SAID LAST EFFECT TO SAID UNIT, MEANS INCLUDING COMPRESSOR MEANS FOR SUPPLYING COMBUSTION AIR AND FUEL TO SAID UNIT FOR COMBUSTION THEREIN, A SUPERHEATER FOR HEATING THE GASES AND VAPORS LEAVING SAID UNIT, A FLASH VAPORIZER RECEIVING CONCENTRATED BRINE FROM SAID UNIT, MEANS FOR SEPARATING FLASHED WATER VAPOR FROM SAID CONCENTRATED BRANE, A HIGH PRESSURE TURBINE DRIVEN BY THE EXPANSION OF THE SUPERHEATED GASES, CONDUIT MEANS FOR SUPPLYING THE EXPANDED GASES FROM SAID TURBINE TO SAID INITIAL EFFECT FOR INDIRECTLY VAPORIZING WATER FROM THE FEED BRINE WITHIN SAID INITIAL EFFECT, MEANS FOR SEPARATING CONDENSATE FROM SAID GASES AND VAPORS LEAVING THE INITIAL EFFECT, AT LEAST ONE LOW PRESSURE EXPANDER, ANMD CONDUIT MEANS FOR SUPPLYING THE GAS AND REMAINING VAPORS TO SAID LOW PRESSUR EEXPANDER FOR ADDITIONAL POWER RECOVERY. 